The invention pertains to a hydraulic elevator with a pressure accumulator acting as a counterweight wherein a first pump conveys hydraulic oil through a pumpline, a valve unit and a cylinder line to and from a hydraulic drive for an elevator car, a second pump conveys hydraulic oil by way of a solenoid valve to and from the pressure accumulator, the hydraulic oil being supplied to and taken from a tank, the two pumps being rigidly connected to each other and driven by an electric motor. The invention further relates to a process for controlling and regulating operation of the elevator.
Hydraulic elevators of the general type in question are suitable for conveying people and goods, for example, between the floors of buildings.
A hydraulic elevator of the general type described above is known from DE-A1 3,040,717. A hydraulic oil can be conveyed by a first pump from a tank to a hydraulic drive unit for an elevator car or from the hydraulic drive to the tank. Hydraulic oil can also be conveyed from a tank to a pressure accumulator or from the pressure accumulator to the tank by a second pump by way of a solenoid-operated valve. The two pumps are rigidly connected to each other and can be driven jointly by means of an electric motor. Thus, when one of the pumps is conveying hydraulic oil, the other pump acts as an auxiliary drive, i.e., as a hydraulic motor. In and of itself, the motor is called upon to provide only the amount of energy corresponding to the difference between the potential energy in the hydraulic drive and that in the pressure pressure accumulator. This has the effect of reducing the energy consumption as long as the potential energies present in the hydraulic drive and in the pressure accumulator are properly adjusted with respect to each other. To control the travel of the elevator car operated by the hydraulic drive, the object of DE-A1 3,040,717 requires two controllable valves, namely, one valve for upward travel and one valve for downward travel. One of these valves is opened slowly when the car is to be started from a standstill or closed slowly when the car is to be slowed before coming to a stop again. The motor driving the pumps is turned off after the car has stopped. A dissipation of energy occurs in each of these servovalves during both the startup and the slowdown phase, during both ascents and descents. This results not only in a waste of energy but also in the heating of the hydraulic oil, which reaches a relatively high temperature. It is known that the behavior of an elevator car is negatively affected by variations in the temperature of the hydraulic oil.
A process and a device for controlling a hydraulic elevator is known from WO-A1 98/34,868, in which the speed and thus the output of a pump, driven by a motor, are controlled and/or regulated. The energy expended to lift the car is present after the ascent as potential energy in the car; and at least some of this energy is recovered during the descent, in that the potential energy of the car is used to operate the pump as a hydraulic motor and the electric motor as a generator. The electrical energy thus produced is either returned by way of a feedback unit to the power system or destroyed by braking resistances.
An object of the present invention is to provide a hydraulic elevator and a method for controlling the elevator which reduces the amount of energy required to operate the elevator. A reduction in the energy expenditure is simultaneously associated with greater economy of operation.
The object of the present invention is achieved by a hydraulic elevator comprising an elevator car with a hydraulic drive. A first pump is connected to the hydraulic drive through a pump line, a valve unit and a cylinder line so that the valve unit is arranged between the first pump and the hydraulic drive. The first pump also being connected to a tank having hydraulic oil. The valve unit includes a controllable valve and a first nonreturn valve connected in parallel with said controllable valve. During operation, the first pump selectively conveys hydraulic oil to and from the hydraulic drive. The hydraulic elevator also includes a pressure accumulator acting as a counterweight. A second controllable valve is arranged between the pressure accumulator and a second pump. During operation, the second pump selectively conveys hydraulic oil to and from said pressure accumulator through said second controllable valve. The first and second pumps are fixedly connected such that when hydraulic oil is conveyed to the hydraulic elevator by the first pump, hydraulic oil is conveyed from the pressure accumulator by the second pump. An electric motor is connected for driving the first and second pumps. A power regulating unit is connected to the electric motor for actuating the electric motor and a control/automatic regulation unit is connected to the power regulating unit and the first and second controllable valves for controlling and automatically regulating a speed of said elevator car by controlling actuation of said power regulating unit and the second controllable valve, and for actuating the first controllable valve during a descent of the elevator car.